Heretofore, in a material gas supply apparatus for semiconductor manufacturing devices and the like, thermal flow rate control devices and pressure-type flow rate control devices are widely used for controlling the flow rates of supplied gases. Especially, as shown in FIG. 6, a pressure-type flow rate control device FCS is constituted by a control valve for pressure control CV, a temperature detector T, a pressure sensor P, an orifice OL, a calculation control unit CD consisting of a temperature correction/flow rate calculation circuit CDa, a comparator circuit CDb, input output circuit CDc, output circuit CDd and other components, and has excellent flow rate characteristics which allow performing stable flow rate control even if the primary side supply pressure greatly varies.
That is, in the pressure-type flow rate control device FCS in FIG. 6, the detection values from the pressure sensor P and the temperature detector T are input into the temperature correction/flow rate calculation circuit CDa, where the temperature correction and flow rate calculation of the detected pressure are carried out, and a flow rate calculation value Qt is input into the comparator circuit CDb. Moreover, an input signal Qs corresponding to the set flow rate is input from a terminal In, and is input into the comparator circuit CDb via the input output circuit CDc, where it is compared with the flow rate calculation value Qt from the temperature correction/flow rate calculation circuit CDa. When, as a result of the comparison, the set flow rate input signal Qs is smaller than the flow rate calculation value Qt, the control signal Pd is output to the drive part of the control valve CV. This drives the control valve CV to the closing direction, and drives to the closed valve direction until the difference (Qs−Qt) between the set flow rate input signal Qs and the calculation flow rate value Qt becomes zero.
In the pressure-type flow rate control device FCS, when a so-called critical expansion condition, that is, P1/P2≥about 2, is retained between a downstream side pressure P2 and an upstream side pressure P1 of the orifice OL, the gas flow rate Q passing through the orifice OL becomes Q=KP1 (wherein K is a constant), while when the critical expansion condition is not met, the gas flow rate passing through the orifice OL becomes Q=KP2m(P1−P2)n (wherein K, m, n are constants).
Therefore, the flow rate Q can be controlled with high accuracy by controlling the pressure P1, and even if the pressure of an upstream side gas Go of the control valve CV is greatly changed, the control flow rate value hardly changes, exhibiting excellent characteristics.
The pressure-type flow rate control device which calculates the gas flow rate Q as Q=KP1 (wherein K is a constant) may be referred to as FCS-N type, and the pressure-type flow rate control device which calculates the gas flow rate Q as Q=KP2m(P1−P2)n (wherein K, m, n are constants) may be referred to as FCS-WR type.
Furthermore, the pressure-type flow rate control devices of this type also include so-called FCS-SN types and FCS-SWR types. An FCS-SN type device uses, as the orifice of the above FCS-N type, an orifice mechanism in which a plurality of orifices OL are connected in parallel, and a gas flows through at least one orifice by a switching valve, e.g., an orifice mechanism in which two orifices are connected in parallel, and a switching valve is provided on the inlet side of one orifice to allow the flow rate control range to be changed by opening and closing the valve, while an FCS-SWR type device uses the same orifice mechanism as an orifice of the above FCS-WR type.
It should be noted that the configurations, operating principles, etc. of the pressure-type flow rate control devices themselves of the above FCS-N type, FCS-SN type, FCS-WR type and FCS-SWR type are already known, and therefore their detailed explanation will be omitted herein (Japanese Unexamined Patent Publication No. H8-338546, Japanese Unexamined Patent Publication No. 2003-195948, etc.).
Moreover, the types of the pressure-type flow rate control device FCS include, as shown in FIG. 7, a pressure-type flow rate control device FCS (hereinafter referred to as FCS-N type. Japanese Unexamined Patent Publication No. H8-338546, among others) which is intended for a gas fluid having a configuration as in (a) under critical conditions, a FCS-WR type which is intended for both gas fluids under critical conditions and non-critical conditions of (b) (Japanese Unexamined Patent Publication No. 2003-195948, among others), a flow rate switch type FCS-S which is intended for a gas fluid under critical conditions of (c) (Japanese Unexamined Patent Publication No. 2006-330851, among others), and FCS-SWR type of flow rate switch type which is intended for both gas fluids under both critical conditions and non-critical conditions of (d) (International Patent Publication WO2009/141947 pamphlet, among others).
It should be noted that in FIG. 7, P1 and P2 denote pressure sensors, CV denotes a control valve, OL denotes an orifice, OL1 denotes a small-diameter orifice, OL2 denotes a large-diameter orifice, and ORV denotes an orifice switching valve.
FIG. 8 is a cross-sectional view which shows a known pressure-type flow rate control device (FCS-WR type), 5A denotes a body, 2 denotes a fluid inlet, CV denotes a control valve for pressure control, P1 and P2 denote pressure sensors, OL denotes an orifice, and 3 denotes a fluid outlet.
However, the pressure-type flow rate control device FCS of this type has poor replaceability of the gas since the orifice OL with a minute diameter is used, and has the problem that the so-called fall response for the gas is extremely poor when the control valve for pressure control CV of the pressure-type flow rate control device FCS is closed and the output side is released as it takes long time to discharge the gas in a space portion between the control valve CV and the orifice OL.
FIG. 9 shows an example of the fall response characteristics at the time of continuous steps of a known pressure-type flow rate control device FCS-N type. When the amount of gas supplied is dropped in a stepwise manner while the gas is being supplied at a certain flow rate via the pressure-type flow rate control device with an air motor valve (not illustrated) on the downstream side of the orifice OL released, in the case of the pressure-type flow rate control device for small flow rates (line B) compared to the case of the pressure-type flow rate control device for large flow rates (line A), it takes 1.5 seconds or more to drop the flow rate to a predetermined level in the current situation.
More specifically, in the case of FCS-N type and FCS-WR type, the downstream side pressure of the orifice OL is 100 Torr, and therefore, in order to drop the flow rate from 100% to 1% and from 100% to 4%, it takes about 1 second or more respectively, but in terms of semiconductor manufacturing devices (for example, etchers), it is required to drop the flow rate from 100% to 1% within 1 second.
Moreover, in the case of the FCS-S type and FCS-SWR type, when the downstream side pressure of the orifice OL1 is 100 Torr, in order to drop the flow rate from 100% to 10% and from 100% to 0.16%, it takes about 1.2 seconds or more respectively, but in terms of the semiconductor manufacturing device (for example, etcher), it is required to drop the flow rate from 100% to 10% within 1.2 seconds.